Why is the sky *any* color?

Discuss

35 Responses to “Why is the sky *any* color?”

  1. anansi133 says:

    Are our eyes evolved to see unfiltered sunlight as “white” then? I have to wonder what our color palette might look like to eyes that evolved under a different star type.

    • JoeBuck says:

       The peak intensity is for green light. So some being that evolved under a red star would probably think of the earth as Emerald City.

      • Sunlight doesn’t really have a “color” and just contains all the frequencies. So our eyes could have envolved to be sensitive to any of the colors. But green must have proven to be the most useful. 

        A red star would lack the green and blue frequencies, so the aliens probably wouldn’t have photoreceptor cells reacting to those frequencies. And be very good at seing red. 

        Also remember that a single frequency usually stimulates all 3 kind of cones and the color we see is constructed from the identities. And the same color can be seen by a different mix of frequencies that stimulate the cones the same way. 

    • AnthonyC says:

      Or a different atmosphere.

    • JoeBuck says:

       You beat me to that one.

    • Drew_Gehringer says:

      answer; It is actually partly violet, your brain’s just weird and perceives a mix of blue and violet light as blue mixed with white.

      • LYNDON says:

        I was about to say there’s no such thing as violet light as such but then I looked it up. Either they put me wrong in design class or I’m just thinking of indigo. Seems there’s a twitch in the response of the red receptors down that end or something, hence the purplish impression?

        I’d assumed no-violet was what xkcd meant because there’s another example of a misleading question in the rollover text https://xkcd.com/1145/

        That said, Wikipedia giving RGB values for Violet then asserting it’s not the same a purple isn’t calculated to reassure the confused. (Of course, I’m not going to satisfy myself about this by looking at a book or a computer screen.)

        Anyway: NASA’s answer to the sky question here http://science-edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html#violet

  2. Timmo Warner says:

    Every fiber of my being wants to upload a version of that video that ends at 45 seconds.

  3. Big Steve says:

    I guess whether Homer used a word for blue depends on what your idea of blue is. This is the word that eventually becomes “cyan”, although it doesn’t refer to what we think of as cyan, but instead is dark blue.

    http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0073%3Aentry%3Dkua%2Fneos&highlight=blue

    • First Last says:

      More importantly, Homer doesn’t describe things in colours, he uses words – including what we recognise as colours – to describe things in qualities. The sky is “bronze” not because it’s brown or tan but because it’s shining and bright; the sea is “wine-dark” because it’s deep and opaque.

      He’s a poet, he’s not going to write “the sky was fucking blue that day man, I swear – REALLY FUCKING BLUE”. His audience know what -colour- the sky is, he wants to evoke what it -looks like-.

  4. I’m not sure if I’d call his explanation wrong, but after seing the video, I wouldn’t have understood it. You might have noticed that if light travels a medium that scatters blue, it will become less blue, not more. Here is why the sky is blue after all: 

    The light traveling from the sun directly to your eyes (the sun itself) is still white. Without scattering, the rest of the sky would be black. But since the air bends the blue light rays, they can still reach earth. 

    The sunset is red mostly because the light is affected by larger particles (clouds, pollution) which scatter more of the red spectrum.

  5. drokhole says:

    Who is the Master that makes the sky blue?

  6. senorglory says:

    BECAUSE I SAID SO! NOW GO CLEAN YOUR ROOM.

  7. timquinn says:

    It’s because we couldn’t afford the wallpaper.

  8. swlabr says:

    I think that the old bard Homer just had a different kinda vocabulary…

  9. Bleach248 says:

    The sky doesn’t have any color, it just looks like it does from where you are looking at it. The sky never changes color, it is the sunlight that does all that.

  10. dioptase says:

    Whenever my kids have asked why the sky is blue or red, I tell them “Rayleigh scattering.”  Best delivered in a deadpan voice without explanation.

    They don’t ask me many questions anymore.

  11. bo1n6bo1n6 says:

    “To make you ask questions.” – exact quote from my mom.

  12. smut clyde says:

    blue is one of the last colors that cultures pick out a word for

    I hope this item of Fail does not become the new colour-linguistics “Eskimo Words for Snow”.

    • billstewart says:

      There’s actually a lot of work out there on how different languages and cultures handle color.  Some languages don’t distinguish as many colors as others do, and they may delimit those colors differently.  For instance, in the Scandinavian languages, the fruit we call an “orange” has a color they call “red”.

      All of that’s independent of what the paint-sellers and crayon-sellers call colors in those cultures, of course :-)

  13. vsherbie says:

    HOLY SHIT!
    I went to grad school with that guy! Small world. 

  14. william beaty says:

    If you shine white light on a single nitrogen molecule, and view it against a dark background, it should look like a tiny sky-blue speck.  (Too small to see?   Nah, just use much brighter light!)

    So, if we hold a single nitrogen molecule up against a bright white background (e.g. light bulb,) it should appear as a dark red-orange shadow; a blotch the color of sunsets.

  15. Nana Aba says:

    “From Greece to Africa to China…” as though they’re all different countries.

  16. ROSSINDETROIT says:

    Speaking of color and language, I’ve read a summary of a study that determined that native speakers of Russian are able to discriminate shades of blue more finely than non-Russian speakers.  Apparently the habitual use of that language also affects a part of the brain dedicated to color perception.  The brain is weird.

Leave a Reply